1. Field
Aspects of the present disclosure relate generally to wireless communication systems, and more particularly, for enabling uplink beamforming transmit diversity channel estimation.
2. Background
Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, 3GPP Long Term Evolution (LTE) systems, orthogonal frequency division multiple access (OFDMA) systems, and high speed packet access (HSPA) systems.
Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more base stations via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. This communication link may be established via a single-in-single-out, multiple-in-signal-out or a multiple-in-multiple-out (MIMO) system.
A MIMO system employs multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas may be decomposed into Ns independent channels, which are also referred to as spatial channels, where NS≦min{NT, NR}. Each of the NS independent channels corresponds to a dimension. The MIMO system can provide improved performance (e.g., higher throughput and/or greater reliability) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized.
Generally, in a closed loop transmit diversity (CLTD) beamforming scheme for cellular systems, where two pilot channels are sent on two eigenmodes (e.g. two orthogonal beamforming vectors), due to fluctuation of beamforming phase and/or amplitude from slot to slot, channel estimation for demodulation by a pilot filter working on a primary pilot channel may observe performance loss.
Thus, improved apparatuses and methods for channel estimation in CLTD beamforming schemes are desired.